Automotive horns are a significant source of urban noise pollution. While automotive horns, including truck horns, can be useful signal devices in an emergency situation, many drivers use the horn habitually to express minor annoyance and anger, for social purposes, and to intimidate other drivers. In response to the noise pollution attributable to automotive horns, some states and municipalities have passed legislation penalizing unnecessary horn use. Enforcement of such legislation is impractical since a police officer is required to identify the vehicle from which the sound originated, determine whether use of the horn was necessary, and then stop the vehicle to issue a citation. In New York City, for example, there are posted notices stating a $350 fine for horn honking, yet one may readily observe that such signs have no discernible effect on driver behavior.